Plastic hydrocolloid composition and method of making



Patented July 11, 1939 UNITED STATES PATENT OFFICE PLASTIC HYDROCOLLOID COMPOSITION AND METHOD OF MAKING No Drawing. Application May 3, 1933, Serial No. 669,198

14 Claims.

Our invention relates to that class of compositions that may be employed for taking impressions and which are particularly applicable in making replica casts of parts of the human body,

and is especially directed to the making of reproductions of the form of the oral cavity.

For many years past it has been common practice in the taking of impressions of the oral cavity to employ gypsum products, such, for instance,

as what is commonly known as plaster of Paris. Obviously, such material sets with unyielding rigidity and therefore can only be withdrawn as a unit where there are present no undercuts such as any relatively inclined teeth would produce.

Consequently, an impression taken with such unyielding material must necessarily be cracked up into pieces such as may be withdrawn, which pieces must be subsequently placed together to form the integral intaglio niold desired from which the replica cast may be produced.

There are other disadvantages in the use of gypsum products among them being the disagreeable feeling experienced by the mud-like plaster contacting with the tissues, that it requires several minutes to set or solidify, and that the breaking up of the cast is likely to injure the permanent denture work that may be in the mouth of the patient.

The principal objects of our invention are to provide a cohesive impression taking and model ciently yielding in its nature to permit its withdrawal as a unit and retain its intaglio form, including all undercuts, with absolute precision.

Other objects of our invention are to produce a plastic hydrocolloid mass so prepared and constituted that it may be employed in the taking of impressions of the mouth without the attendant undesirable efiect on the tissues and denture work, and that in its solidified state serves asan intaglio mold in which plaster casts may be molded without interference with the setting of the plaster and without tendency of the plaster to adhere thereto. Or, to state it the other way around, our hydrocolloid composition when solidified is in adhesive toward plaster, so that a mold formed of the composition does not stick to a plaster cast molded therein Further objects of our invention are to provide a plastic hydrocolloid composition for forming molds for plaster casts with an accelerating 5 agent tending to accelerate the setting of the plaster molded therein and thereby counteracting the normal retarding action of the mold forming material upon the set of the plaster forming the cast by its contact with the mold.

Our invention also comprehends a plastic hydrocolloid composition for forming molds, which has incorporated therein a precipitating agent or fixing substance the excess of which is susceptible of being removed by washing, and a basic substance added to neutralize any traces 10 of said precipitating agent or fixing substance which might remain after washing, and which may progressively react with the other constituents of the hydrocolloid, destroying their. jelly forming ability; This is more fully ex- 15 plained hereinafter.

As ordinarily prepared, compositions (other than plaster of Paris, and the like), for use in forming molds, such as those which yield for making plaster casts, have a tendency to inter- 2o -fere with the set of the cast forming material such as plaster of Paris, alpha-gypsum, Keenes cement, etc. When poured against the surfaces of the mold for the purpose of making casts or models, so that adhesion of the plaster or other 25 ingredients employed occurs with the result of producing rough and inaccurate models or casts.

In some instances, particularly where a reversible hydrocolloid material is employed, fixing agents, such as alum and tannic acid, have been sug- 3o gested to prevent such adhesion.

We have found that the simple addition of fixing substances either does not satisfactorily remedy the difficulty, or .deleteriously affects the properties of the material to such an extent' 35 either whenfreshly made or shortly thereafterthat it becomes unsuitable for the purpose intended, or at least its efliciency is found to be greatly impaired.

We have discovered after considerable research 40 andexperimentation that the chief cause of the adhesion of the plaster forming the cast is the soluble organic substances present in the hydrocolloid of which the plastic composition is largely composed, which tend to retard the setting of the 45 plaster forming the cast.

Our plastic hydrocolloid impression composition may be produced from a reversible hydrocolloid such as agar agar, water, glycerin or sugars, fatty substances, waxes and the like,-oils, resins, vegetable fiber, mineral fillers, antiseptics, flavoring agents and substances designed to accelerate the set of plaster of Paris orv other material employed to form the cast, said plaster set accelerating substances being employed to counteract reaction of the retarding matter inherent in the agar agar type of hydrocolloid, which normally tends to retard the set of plaster of Paris, or other material, forming the cast.

A composition that has been found to be satisfactory may be compounded as follows:

Agar -10 parts (reversible hydro- I R colloid). Parafiin wax 5 parts (wax). Mineral oil .1 part (oil). Common rosin JA; part (resin). Cotton fiber part (vegetable fiber). Blane fix l0 parts (mineral filler). Phenol or other antiseptic part (antiseptic). Flavoring oils part (fiavor) Potassium sulfate -.l part (accelerator). Water, q. s. to make 100 parts.

We have found that by washing the agar with cold water to remove the major portion of the organic substances that retard the setting of the plaster cast and by adding plaster setting accelerators to the mass to counteract or neutralize the effect of the remainder, satisfactory results may be obtained. Satisfactory results may also be obtained by adding chemical substances which react with and thus counteract the interfering organic substances, and preventing the action of these added substances on the other constituents of the agar by having present in the mixture, or subsequently adding thereto, a second protective agent or substance which arrests the deleterious action of the first on the other constituents of the agar but which does not arrest or reverse the action of the first on the interfering organic substances. In particular, the agar may be treated with a solution of a precipitating or fixing substance to fix or precipitate the interferent substances, subsequently washing the agar to remove excess and neutralizing any traces remaining, which might react on the jelly forming constituents of the agar'to their detriment, by adding to the mixture a substance which arrests the deleterious action of the precipitatory or fixing substance on the other constituents of the agar but which does not arrest or reverse its action on the interfering organic substances. By either washing the agar agar hydrocolloid or treating it with a precipitating or fixing agent (as just described), the plaster-set-retardant matter which it includes is to all intents and purposes e1iminated,to a degree depending on the thoroughness of the washing, or on the sufficiency of the precipitant to counteract the retardant matter. In either case, therefore, the agar is pro tanto freed of the retardant matter as such.

By fixing or precipitating substance is meant the provision of a substance capable of rendering the interferent substances innocuous either by combining therewith and providing a product which can be physically separated by precipitation or otherwise from the residue of the jelly, or by providing therewith a product which may remain in the jelly but does not have the capability of retarding the setting of plaster, or by producing a conjoint action with the retardant substances which compensates for this action.

In washing the agar agar, the agar agar is soaked in 160 parts of cold water until it softens and swells. The water is then drained off and replaced by fresh water. This operation may be repeated several times, or washing may be accomplished by passing a continuous current of This removes about by weight of the agar which includes most of the substances present which exert a retarding action on the setting of the cast of plaster or other materials employed. The prolonged treatment of the agar with water as described-whether. by repeated soakings, or in a continuous current-removes the deleterious retardant matter by dialysis, rather than by washing in the ordinary sense: i. e.,' the watersoaked mass of agar behaves like a dialysing diaphragm or sack enclosing the impurities, which as they dissolve diffuse out through the wet agar into the surrounding water.

It is difficult to wash the agar free from all the offending substances without prolonged washing and excessive loss of material. Instead of doing so we may add to the compound which includes the washed agar a small quantity of a plaster set accelerator, such as potassium sulfate or other suitable substance. Obviously, other materials which are known to accelerate the set of plaster may also be used, for instance, magnesium sulfate, ferrous sulfate, various alums and other double salts, sodium chlorid, potassium chlorid, and a variety .of other soluble sulfates and chlorids, with varying degrees of efficiency.

The washed agar is dissolved by boiling with 150 to 200 parts water. When solution is complete, it is boiled and stirred to get rid of excess water. When about 100-120 parts of water remain, the wax, resin and mineral filler hereinbefore referred to are added. The solution is violently agitated and the wax and resin added in the molten condition so that an emulsion is formed. The grain of the emulsion may be improved by passing it through a colloid mill.

Heating and stirring is continued while the cotton fiber is added and until all excess water is' driven off, The plaster setting accelerator, such as potassium sulfate in solution in a small quantity of water, is then added. The mix is then cooled slightly and the flavoring material and the antiseptic added. After thorough mixing, the mass is allowed to cool and is then ready to package for sale. The accelerator is preferably added when the batch is nearly complete, so as to minimize any action it might have on the compound during the process of manufacture.

As already mentioned, the retarding action of the constituents of plastic hydrocolloid impression materials of the kind above described may be neutralized, by adding to them substances which react with the retarding constituents, precipitating or fixing them. The addition of such substances effectively prevents the undesirable action of the compound on the plaster cast, particularly if the added material is also an accelerator of the setting of the model material used,

However, such substances, if present in suflicient quantity to accomplish the desired results, react with the jelly-forming constituents of the agar, commonly called pectin and gelose, and materially reduce or destroy the strength and elasticity of the jelly produced on cooling the'mass. This action is progressive and is acceleratedzby increasing the temperature.

Thus, if the precipitating agent is added to the mass early in the process of manufacture and is present while the mass is being boiled to expel excess water, it will act on the agar to such an extent that the finished compound will not set to a jelly on cooling. If it is added near the end of the process, its action will be less and the aicaeso freshly made material will form a satisfactory jelly. On keeping at room temperature for some time and reheating for use, it will be found that the jelly strength is progressively reduced as the time of storage is increased.

We have found that the action of the pre--- cipitating and fixing agent on the pectin and gelose depends upon the acidity of the medium and that by adding to the mass the oxid, hy-

droxid or carbonate of a basic substance of such properties and in such quantities that the acidity is reduced during the process of manufacture to a value such that the pH determined by the usual methods is between 6 and 8, pref erably between 6.5 and 7.5, the precipitating and fixing effect is accomplished and the deleterious action of the added substance upon the jellyforming constituents of the agar is prevented.

- We have found that the added basic substance acts most efficiently when added in the form of small particles, which particles are almost insoluble in water. Examples of sparingly soluble basic substances that may be added are carbonates of calciumpbarium, strontium and magnesium, oxids or hydroxide of cobalt, nickel, zinc, cadmium, magnesium, beryllium and manganese. Such substances may be generally referred to as (basic) metal'oxide agents, for reasons obvious to chemists.

' Examples of are the sulfates (and double sulfates with the alkali metals) of iron, chromium, aluminium,

- zinc, nickel cobalt, cadmium and manganese and the chlorids, nitrates and acetates of the same metals. 1 1

The basic substa ce may beadded before the precipitatiii fixing substance; or afterwards, "or at the sa e' time'; depending uponthe amount of. action ;'o r; ne precipitating substance on the gelose and that: .is desired 1 or permitted.

It must.be-}added2in,excess. The quantity of added-substance that constitutes an excess de pends upon the quantityof-precipitating and fix- -;potash alum'=is-added,- 95 calcium carbonate f or pigment used.

ingagentused andxuponthe acidity it produces in the masagj'lhua'if 1%.zinc sulfate is added tothe compound as a precipitating agent,

zinc oxide is 'a' sufficient excess, while if 1% The basic oxid be added 'in great excess and mayreplace all or part of the mineral filler The precipitating and-fixing substance may be added at any time during'the process of manu--. facture. The quantity of precipitating and fix ing agent required depends upon the quantity of substances interfering with the set of plaster, etc., present in the agar.

- washing, a correspondingly smaller quantity of precipitating and fixing substance is required than if unwashed agar is used. We have found .that additions from a minimum of %o% to a maximum of 2% have been sumcient to produce the desired results. Exact proportions in a given case must be found by, experiment.

For thus neutralizing the effect-of substances contained in the agar on the set of plaster the agar may be treated in the cold with the precipitating and fixing substances,

In the following manner the agar is soaked for 12-24 hours in a solution of the precipitating and fixing substance at a temperature below -F.'

and then washed to remove the excess of pre-,

cipitating and fixingsubstance which might have deleterious action on the jelly forming constituprecipitating and fixing agents ties of any such .removed. 4

If this is reduced by' cuts of the agar. As a, final step, a basic substance such as those described above is added to neutralize any traces which might remain after washing. The precipitating .and fixing agents used are those described above and, in addition,

tannic acid, tannin, and formaldehyde. The

precipitating and fixing agent can be used as a solution varying in strength from a minimum of io% to the maximum of a saturated aqueous solution of the agent used. The basic substance must be present in excess, as described above.

We have found that- A t0 2% of the weight tion contemplated is much less irksome to both the patient and operator alike, as such composition greatly facilitates the operation and saves time, discomfort and expense ,'and produces more accurate results than by compositions heretofore known.

'It is obvious that the invention is notlimited .to the specific material stated; but that it maybe employed in many ways within the scope of the appendedclaims.

' Having thus described our invention, we claim: 1; A, method for preparing an improved plastic hydrocolloid composition, for taking impressionsand forming molds for plaster casts, said composition-comprising as its base'a plastic agaragar hydrocolloid including plaster-set-retard- .ant organic matter; which method comprises ,'washing the commercially pure hydrocolloid' with cold wateruntil substantially 20 percent of the substance thereof has been removed and therewith the major portion or such organic matter, and adding to the hydrocolloid an agent effective forneutralizing the retardant properorganicmatter remaining un- 1 2. A method forpreparing an improved plastic hydrocolloidcomposition, for taking impressions and forming molds for, plaster casts, said composition comprisingas its base a plastic agaragar hydrocolloid. including plaster-set-retardant organic matter;v which} method comprises washing the commercially pure hydrocolloid with cold water until substantially 20 percent of the substance thereof has been removed and therewith the major portion' of such organic matter, and adding to the treated hydrocolloid anagent effective for neutralizing the'retardant properties of any such organic matter remaining unremoved, said agent comprising a soluble sulphateor chloride.

' 3. A method for preparing'an improved plastic hydrocolloid composition, for. taking impressions and forming molds for plaster casts, said composition comprising as its base a plastic agaragar hydrocolloid including plaster-set-retard ant organic matter; which method comprises washing the commercially pure hydrocolloid to eliminate a portion of such retardant organic matter, and adding to the hydrocolloid a reagent effective for neutralizing the retardant properties of any such organic matter remaining unremoved, which reagent tends to act deleteriously on the jelly-forming constituents of the bydrocolloid, and adding a neutralizing agent for preventingdeleterious action of such reagent on the hydrocolloid composition.

4. A method for preparing an improved plastic hydrocolloid composition, for taking impressions and forming molds for plaster casts, said composition comprising as its base a plastic agaragar hydrocolloid including plaster-set-retardant organic matter; which method comprises washing the crude hydrocolloid to eliminate a portion of such retardant organic matter, and adding to the hydrocolloidfa soluble metal salt eiiective for neutralizing the retardant properties Many such organic matter remaining unremoved; which salt tends to act deleteriously on the jelly-forming constituents of the hydrocolloid, and adding a basic metal oxide agent for preventing deleterious action of such salt on the hydrocolloid composition. I

5. A method of producing an improved, inadhesive plastic composition for taking impressions and forming molds for plaster casts, of the type characterized by a base of reversible hydrocolloid which includes plaster-set-retardant matter; which method comprises treating the hydrocolloid with a precipitating agent for its said plaster-set-retardant matter, which agent tends to act on its jelly-forming constituents; washing the treated hydrocolloid and thereby removing therefrom unreacted'precipitating agent; and adding to the treated and washed hydrocolloid an agent tending to arrest the action of said precipitating agent on jellyforming constituents of the hydrocolloid.

6. A method for preparing an improved plastic hydrocolloid'composition, for taking impressions and forming molds for plaster casts, said composition comprising as its base a plastic agaragar hydrocolloid including plaster-set-retardant organic matter; which method. comprises washing the agar-agar with cold water and adding thereto zinc sulphate and zinc oxide.

7. An improved, inadhesive plastic composition for taking impressions and forming molds for plaster casts, comprising a base of reversible plastic agar-agar hydrocolloid which has been washed with cold water until substantially 20 percent of the jelly-forming constituents have been eliminated and therewith the major portion of plaster-set-retardant matter naturally present in the crude agar-agar, and also comprising onetenth to 2 percent of an agent for counter act-. ing the retarding effects of any unremoved remainder of such retardant matter.

8. An improved, inadhesive plastic composition for taking impressions and forming molds for plaster casts, comprising a base of reversible plastic agar agar hydrocolloid which has been freed of the major portion of plaster-set-retardant matter naturally present in the crude agaragar, and also comprising a reagent for counteracting the retarding eifects of any unremoved remainder of such retardant matter, said reagent tending to act deleteriously on the remaining jelly-forming constituents of the hydrocolloid,

amaeso colloid base, a soluble metal salt for counteracting such matter, which salt-tends to act deleteriously on the jelly-forming constituents of the hydrocolloid base, and a proportion 01 basic neutralizing agent such that the pH oi the composition lies between 6 and, 8, said neutralizing agent being eilfective to arrest the action of said metal salt on the jelly-forming constituents of the hymetals which include also an alkali metal base,

said reagent tending to act deleteriously on the hydrocolloid base, and a basic metal oxide neutralizing agent for preventing deleterious action of 'said precipitating or fixing reagent upon the hydrocolloid base selected from the group consisting of the carbonates of alkaline earth metals and the oxides and hydroxides of cobalt, nickel, zinc, cadmium, magnesium, beryllium and manganese.

11. An improved inadhesive plastic composition for taking impressions and-forming molds for plaster casts, of the type characterized by a base of agar-agar hydrocolloid which naturally includes plaster-set-retardant matter; said composition comprising, besides the hydrocolloid base, alum and zinc oxide. 1 v

12. An improved, inadhesive plastic composition for taking impressions and forming molds for plaster casts, of the type characterized by a base of agar-agar hydrocolloid which naturally includes plaster-set-retardant matter; said composition comprising, besidesthe hydrocolloid base, zinc sulphate and zinc oxide.

13. An improved, inadhesive plastic composition for taking impressions and forming molds for plaster casts, of the type characterized by a base of reversible plastic agar-agar hydro-' 'agent for preventing deleterious action of the metal salt on the hydrocolloid base.

14. An improved, inadhesive .plastic composition ior taking impressions and forming molds for plaster casts, of the type characterized by a base of reversible plastic agar-agar hydrocolloid which naturally includes plaster-set-retardant matter; said composition comprising, besides the hydrocolloid base, fatty substance, resin, antiseptic, flavor, vegetable fibre, and water, together with an agent for counteracting such retardant matter, said agent tending to actdeleteriously on the hydrocolloid base, and a protective agent for preventing deleterious action of the firstmentioned agent of the hydrocolloid base.

J. WALTER H. STANGENBERG. WALTER S. CROWELL. C. VICTOR GROSS.

- CERTIFICATE 6F. CORRECTION. v Patent No; 2,165,680.- I 7 July 11', 19 9.

' JQHAN WALTER n. STANGENBERG, ET AL.

1; is hereby. certified that error appears in the printed. specification of the above nmnbereipetent requiring correction as follows: Page 1 sec- I 0nd column, line 25, for "etc. Qhen" read etc-.-,' when; page 5 Ifirst colmm, line 69, after "substances," insert the words and'period in the following manner line Z0, for" "In the following nenner the" read The; and

that the said Letters Patent should be read with this correction therein that the same may conform to the record of the casein the Patent Office.

Signed. and sealed this 19th day of September, A D. 1959.-

. Henry Van Arsdale (Seal) Acting Commissioner of Patents. 

